Commonly known in the art in the fabrication of the heat exchangers, straight tubes are bent in an approximate range of bend angles of 170° and 190° so as to form a unitary construction of two straight tube sections integrally connected with a return bend formed at a selected bend angle. A skilled artisan would appreciate that if the straight tube is bent precisely 180°, the two straight tube sections would extend parallel to one another while if the straight tube is bent at a selected bend angle anywhere in the approximate range other than 180°, the straight tube sections would extend generally parallel with one another. For simplicity, the term “generally parallel” shall refer to the relationship of the two straight tube sections after the straight tube is bent at any selected angle in the approximate range of 170° and 190° including the precise bend angle of 180°.
By way of example only, variations of a conventional heat exchanger are illustrated in FIGS. 1-6. Although not by way of limitation, a conventional heat exchanger 100 in FIG. 1 includes an upper inlet manifold 102 and a lower outlet manifold 104. A skilled artisan would appreciate that the inlet manifold and the outlet manifold can switch locations such that the inlet manifold is located at the bottom of the conventional heat exchanger 100 and considered a lower inlet manifold while the outlet manifold is located at the top of the conventional heat exchanger 100 and considered an upper outlet manifold. The manifolds 102 and 104 are held in place by a bracket 106a on a side wall 108a. Inlet and outlet fluid conduits 110 and 112 extend through the side wall 108a and communicate with the upper and lower manifolds 102 and 104 respectively. A plurality of serpentine heat exchanger tubes 114 are connected between the upper and lower manifolds 102 and 104. The serpentine heat exchanger tubes 114 are arranged relative to each other in a vertically-staggered array as illustrated in FIGS. 2A, 3A and 4.
Each serpentine heat exchanger tube 114 includes a plurality of straight tube sections 116 and a plurality of return bends 118. The plurality of straight tube sections 116 are arranged in a plurality of generally parallel rows and disposed in a common plane as is known in the art. The plurality of return bends 118 are connected to the plurality of straight tube sections 116 in a manner such that a respective one of the return bends 118 connects sequential ones of the plurality of straight tube sections 116 to form a serpentine configuration. To support the serpentine heat exchanger tubes 114, horizontally extending support rods 120 are mounted on brackets 106a and 106b. A respective one of the brackets 106a and 106b is mounted on respective ones of the side walls 108a and 108b. 
Various cross-sectional configurations of the serpentine heat exchanger tubes 114 as is known in the prior art and any selected ones of the various cross-sectional configurations can be employed as shown in FIGS. 2A-6. In FIGS. 2A and 2B, the cross-sectional configuration of the serpentine heat exchanger tubes 114 is circular. Specifically, both the straight tube sections 116 and the return bends 118 are circular in cross-section. By way of example, the circular cross-sectional serpentine heat exchanger tubes 114 occupy an imaginary heat exchange box B. As best shown in FIG. 2B, consecutive ones of the serpentine heat exchanger tubes 114 contact each other at juxtaposed return bends 118 at respective points Pt.
In FIGS. 3A and 3B, the cross-sectional configuration of the serpentine heat exchanger tubes 114 is partially circular and partially elliptical. Specifically, the straight tube sections 116 are elliptical in cross-section and the return bends 118 are circular in cross-section. As shown in FIG. 3B, consecutive ones of the serpentine heat exchanger tubes 114 contact each other at juxtaposed return bends at respective points Pt.
In FIGS. 4-6, the cross-sectional configuration of the serpentine heat exchanger tubes 114 is generally circular. Specifically, the straight tube sections 116 are circular in cross-section and the return bends 118 are primarily circular in cross-section. The return bends 118 are considered primarily circular because each return bend includes at least one dimple 122 that defines a recess 124 formed into the return bend 118 as best shown in FIG. 6. In FIG. 4, the recess 124 is sized to receive a portion of the adjacent return bend 118 in such a manner that surface-to-surface contact is made between contacting return bends. Such surface-to-surface contact slightly reduces heat exchange capacity of the heat exchanger incorporating this structure and might result in corrosion at a level greater than point contact between contacting return bends. However, this design provides a higher density of packing of the serpentine heat exchanger tubes 114 into an identical space of the heat exchanger packed with circular serpentine heat exchanger tubes 114. By way of example, the circular cross-sectional serpentine heat exchanger tubes 114 in FIG. 2A occupy and define the imaginary heat exchange box B. In FIG. 4, the four heat exchanger tubes 114 are packed in the imaginary heat exchange box B sized identically as the one in FIG. 2B. One of ordinary skill in the art would appreciate that the structure in FIG. 4 is more densely packed into the imaginary heat exchange box B because the recesses 124 formed by the dimples 122 in the respective return bends 118 receive the juxtaposed contacting one of the return bends 118.
Because the heat exchanger tubes 114 are more densely packed in the imaginary heat exchange box B, more heat exchanger tubes can be added to an identically-sized heat exchanger thereby increasing heat exchange capacity.
It would be advantageous to provide a heat exchanger incorporating serpentine heat exchanger tubes that result in a densely-packed heat exchanger. It would be advantageous to provide a heat exchanger incorporating serpentine heat exchanger tubes that provides point contact with consecutive ones of the return bends while simultaneously providing a densely packed heat exchanger. The present invention provides these advantages.